External Abdominal Oblique

The external abdominal oblique muscle (Figs. 1.6,1.7) is the most superficial abdominal muscle that originates from the external surfaces of the lower seven or eight ribs and interdigitates with the serratus anterior and la-tissimus dorsi muscles. Most of the muscle fibers run downward and medially, forming an aponeurosis near the lateral border of the rectus abdominis. The muscle fibers from the lower two ribs descend vertically downward to attach to the iliac crest. Muscle fibers are rarely found inferior to the line that connects the umbilicus to the anterior superior iliac spine. The vessels and nerves that supply the abdominal wall are contained in the double fascial layer that covers the internal surface of the external abdominal oblique and the external surface of the internal abdominal oblique muscle.

The portion of the muscle that inserts into the outer margin of the iliac crest has a free posterior border, which forms the anterior wall of the inferior lumbar tri-gone of Petit. This trigone is bounded anteriorly by the external abdominal oblique muscle, posteriorly by the latissimus dorsi, and inferiorly by the iliac crest. It is a weak zone in the abdominal wall can that tends to her-niate (Petit's hernia), and the hernial sac is usually broad and less likely to incarcerate.

Three different groups of arteries were identified in a study conducted by Schlenz et al. [18] as the sources of blood supply to the external abdominal oblique. The cranial part of this muscle is supplied by the intercostal arteries. In 94.7% the deep circumflex iliac artery and in 5.3% the iliolumbar artery is responsible for the blood supply to the caudal of the muscle. The lateral branches of these arteries run on the outer surface of the muscle, while the anterior branches enter the muscle from its inner surface. Arterial injection studies conducted by Kuzbari et al. [19] have also confirmed the significant contribution of the deep circumflex iliac artery to the blood supply of the external abdominal oblique muscle.

The aponeurosis of the external abdominal oblique (Fig. 1.7) runs anterior to the rectus abdominis and joins the aponeurosis of the internal and transverse ab-dominis at the linea alba. The linea alba is a tendinous midline raphe that extends between from the xiphoid process to the symphysis pubis and pubic crest. It is wider above the umbilicus, separating the recti completely. However, this demarcation may not be easily felt inferior to the umbilicus. As a fibrous structure, it is virtually a bloodless line along which a surgical incision can be made. The triangular part of the linea alba that attaches to the pubic crest is known as the admi-niculum linea alba (Fig. 1.8).

Inferiorly, the external oblique aponeurosis attaches to the pubic tubercle, pubic symphysis and crest. The aponeurosis infolds backward and slightly upward upon itself between the anterior superior iliac spine and the pubic tubercle to form the inguinal (Poupart) ligament (Figs. 1.6,1.7). This ligament, which measures approximately 15 cm, marks the transition between the abdominal wall and thigh. Its curved surface constitutes the floor of the inguinal canal, and maintains an oblique angle to the horizontal.

The reflected part of the inguinal ligament is represented by the fibers of the external oblique aponeurosis that course superiorly and medially to join the rectus sheath and linea alba (Figs. 1.9,1.10). This ligament extends from the lateral crus of the superficial inguinal ring toward the linea alba anterior to the conjoint tendon.

A medially and horizontally aligned extension of the inguinal ligament, which is best seen from the abdominal side, extends posterolaterally to attach to the medial end of the pecten pubis and is known as the lacunar (Gimberant's) ligament (Figs. 1.7, 1.8). This triangular ligament (pectineal part of the inguinal ligament) measures 2 cm from base to apex, and forms the medial border of the femoral canal, separating it from the femoral vein. A second lacunar ligament, known as the fas-cial lacunar ligament, can be seen as an extension of the fascia lata that joins the inguinal ligament, pectineal fascia and the periosteum of the pecten pubis, and receives fibers from the transversalis fascia. The fascial lacunar ligament forms a thickening around the femoral sheath. It is approximately 1 cm anterior and inferior to the pecten pubis and 3 cm lateral to the pubic tubercle.

The superficial inguinal ring (Fig. 1.7), the outer opening of the inguinal canal, appears superior to the inguinal ligament and superolateral to the pubic tubercle. Although the superficial inguinal ring does not as a rule stretch beyond the medial third of the inguinal ligament, it shows some variation in size. In the female it is usually much smaller, accommodating the thin round ligament. The base of the superficial inguinal ring is at the pubic crest and its sides are formed by the medial and lateral crura. The thin medial crura inter-digitate anterior to the symphysis pubis while the much stronger lateral crus attaches to the pubic tubercle. Intercrural fibers cross the apex of the superficial inguinal ring and resist widening of this gap. As the spermatic cord passes through the superficial inguinal ring, it rests upon the lateral crus and becomes invested by the external spermatic fascia, which is an extension of the external abdominal aponeurosis.

A robust fibrous band, the Cooper's ligament, extends laterally along the sharp edge of the pecten pubis and connects the base of the lacunar ligament to the pecten pubis. It receives fibers from the pectineal fascia and adminiculum albae (lateral extension from the lower end of the linea alba) and is considered as a firm structure to which sutures can be anchored. The findings of Faure et al. [20] and Rousseau et al. [21] emphasized the role of the ligament of Cooper in laparascopic surgery of the inguinal region and female urinary incontinence. They confirmed the fact that this ligament is a thickening of the pectineal fascia rather than the periosteum. In McVay's technique of repair of inguinal hernia [22, 23], the Cooper's ligament is sutured to the transversalis fascia. The close proximity of this ligament to the femoral vessels must always be remembered.

As the inguinal ligament runs from the anterior superior spine toward the pubic tubercle, it leaves a posterior gap occupied by vessels and nerves that supply the thigh (Fig. 1.8). This gap is divided by the iliopectineal arch, a septum continuous with the iliopsoas fascia and inguinal ligament into vascular (lacuna vasorum) and muscular (lacuna musculorum) compartments. The vascular compartment contains the femoral vein and artery, and the femoral ring, whereas the muscular compartment encloses the femoral nerve and iliopsoas muscle.

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